1. Field of the Invention
The present invention relates generally to an apparatus and a method for measuring a position, and more particularly, to an apparatus and a method for measuring a position by using a Global Positioning System (GPS) and visible light communication.
2. Description of the Related Art
Position measurement technology is used by an application system and provides a service of accurately detecting a position of a person or an object, which is a target of attention, and using the detected position. Position measurement technology has been developed and used in various ways depending on an applied method or range, and may include, for example, a GPS, an Assisted GPS (A-GPS), and the like.
IGPS corresponds to a currently operated global satellite navigation system. A GPS receiver receives microwaves transmitted from twenty-four or more satellites rotating at a medium earth orbit, thereby allowing a position vector of the receiver to be determined. Specifically, the GPS receiver receives signals transmitted from three or more GPS satellites, and positions of the satellites and the receiver are determined. A distance between the satellite and the receiver may be calculated by measuring a time difference between the signal transmitted from the satellite and the signal received by the receiver. The transmitted signal contains information on the position of the satellite. When distances from a minimum of three satellites and a position of each satellite are provided, the position of the receiver may be calculated using a method such as trilateration. In general, GPS determines a position by using four or more satellite signals in order to correct an error.
A-GPS corresponds to a technology of measuring a position by receiving position measurement auxiliary information from a mobile communication network or wireless Internet (e.g., Wireless-Fidelity (Wi-Fi)), as well as a GPS signal. A-GPS includes an assistance server containing information on a GPS satellite capable of regionally communicating from a closest distance. The assistance server records satellite information, and calculates and corrects a position corresponding to functions required by a position measurement apparatus, such as, for example, a GPS terminal or the like, instead of the position measurement apparatus. When the GPS terminal has difficulty receiving the GPS signal, A-GPS enables position measurement by receiving satellite information from the assistance server through a mobile communication network or a wireless Internet network. By using A-GPS, it is possible to measure a position in a shadow area by receiving satellite information, and to reduce an “initial position information reception time” (Time To First Fix (TTFF): a time taken while a current position of the terminal is detected), so that position information may be rapidly calculated. Accordingly, A-GPS is widely used together with GPS.
However, position measurement technology using GPS has difficulties measuring a position in a shadow area, such as, for example, an urban area having many tall buildings that block a satellite signal. Further, since a GPS receiver requires a large amount of power to receive a GPS satellite signal in the shadow area, a portable device or the like, having limited power may reduce its effective time due to excessive power consumption. Accordingly, although A-GPS technology is used to measure a position in the shadow area using GPS, the A-GPS also receives satellite information through a mobile communication network or a wireless Internet network. Thus, the position measurement apparatus requires a separate communication module, such as a mobile communication module for mobile communication or a Wi-Fi module for wireless Internet communication.
Visible light communication uses light within a visible light wavelength area. The visible light communication, which mainly uses a Light Emitting Diode (LED) as a light source for communication, has received increasing interest due to depletion of the Radio Frequency (RF) band, crosstalk possibility between various wireless communication technologies, increases in a demand for communication security, and the like.
Visible light communication is performed when a visible light transmitter transmits a visible light by using an LED or a Laser Diode (LD) as a light source, and a visible light receiver receives the visible light by using a Photo Detector (PD) and processes a received visible light signal. The LED can flicker at a high speed. When the LED flickers at a high speed, a human's eye cannot recognize the flickering. The visible light communication may use the LED as a light source of an additional communication device while using the LED for its inherent function. Further, as LED emission efficiency has been improved and a cost thereof has been reduced, the LED is becoming more common in a general illumination market which includes a fluorescent light, an incandescent light and the like, as well as a special illumination market for a portable device, a display, an automobile, a traffic light, a signboard and the like. Accordingly, the possibility of application of visible light communication is increasing in various fields where the LED illumination is installed.